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The first of which entails that new top. The M4 Convertible gets a three-part metal roof some 2dB quieter than that of the outgoing M3 Convertible, one that can be raised or lowered at speeds of up to 8mph in 20 seconds.

Then there's BMW's take on the Mercedes “air scarf”, here labelled “Air Collar”. It's a fan mounted between the head-rest and upper seat bolster to keep your neck warm when the roof's down.

The whole car is 60kg (132lbs) lighter than the outgoing, V8-engined BMW M3 Convertible, though still clocks the scale at a not-inconsiderable 1,750kg – the standard M4 Coupe weighs 1,500kg – despite the liberal use of aluminium (the bonnet, front wings and some chassis components), along with carbon-fibre reinforced plastic for the propeller shaft and strut brace.

There's nothing liberal about the engine, mind. It's the same twin-turbocharged, 3-litre straight-six as the new M4 Coupe and M3 sedan, producing the same 431bhp and 406lb-ft of torque.

Obviously that weight penalty means there's a mild performance deficit: zero to 62mph in this M4 Convertible takes 4.6 seconds with the standard-fit manual gearbox (4.3 seconds for the Coupe), or 4.4 seconds with the optional, £2,645 dual-clutch auto transmission (4.1 seconds for the Coupe). Should you care about such things, BMW claims 32.5mpg and 203g/km of CO2 for this auto box. The manual gearbox fares a little worse.

You get an active differential, DSC – including an M dynamic mode – and adaptive M suspension with three modes (Comfort, Sport and Sport+), though there's no mention of the Coupe's Smokey Burnout function. Yes, that's a real thing.

Inside there are electrically adjustable heated leather seats, an M steering wheel, individual rear seats and some boot space: 370 litres with the roof closed, 220 litres with it open/stowed. Outside there are 19in wheels, that “powerdome” bonnet, a really shouty front apron, side gills and air breathers and of course, the quad exhaust pipes.

Prices start at £60,730, and it'll go on sale in the UK on 6 September 2014.